1. Field of the Invention
The present invention relates to a power feed system in a transmission line, and more particularly, to a system having a power feed line switching circuit by which a power feed to a repeater and a switch-over operation to a both-end power feed mode or to a single-end power feed mode are carried out in a Y-shaped transmission line between terminals of a three-terminal station.
2. Description of the Related Art
As submarine fiber-optic cable can carry multiple transmission paths, it is now possible to conceive of a device which allows physical separation of the fiber paths and the subsequent routing of these paths to different landing points. Such a device has the capability of switching power from shore such that in case of a branch failure which might be caused by surface activities such as fishing, etc., the service on the other branches can be maintained. The device also can be capable of switching incoming transoceanic signal paths between shore-end cables so that a full transoceanic capability can be maintained in the event of such a failure.
A branching repeater for the transmitting line fiber-optical undersea cable system for use in a transatlantic cable has been designed, and this branching repeater can connect a cable from one country with branches going to other countries, and can be installed off-shore from the other countries.
This branching repeater is expected to be capable of switching a high voltage power so that the transatlantic circuits can be restored in the event of a cable failure in any branch. The branching repeater is capable of a remote reconfiguration of the internal interconnection to allow for such contingencies as rerouting transatlantic traffic to one branch leg in the case of a failure in the other leg, providing a loop-back to locate faults, switching to a standby line for the transmission line, and easier testing during installation of the branching repeaters and associated links.
The branching repeater can regenerate the three cable spans which enter the device.
In this repeater, as much SL line repeater hardware (See IEEE Vol. SAC-2, No. 6, P. 929, Nov. 1984) as possible is used to minimize the design effort, as well as a plurality of power supply circuits and regenerators. The circuits having power supply circuits and regenerators are the same as those used in the repeater. Note, other supervisory circuits will be seen, but these circuits use the same hardware as the repeater.
The concept of providing power to an undersea cable system is that of supplying an accurately-controlled direct current to the conductor of the cable; wherein each repeater is connected in series to the conductor and develops the necessary biasing voltages through power separation filters and zener power diodes. This is accomplished by impressing a high DC voltage on the conductor at one shore station and a negative DC voltage on the conductor at another station.
FIG. 1A is a diagram showing an example of a power feed system for three-path power feed. A branching point is installed between three terminal stations A, B, and C, to carry out a power source feed for each repeater. Each power feed line is connected to the ground at a branching point to carry out a power feed at each terminal station.
The potential level between terminal stations A and B in FIG. 1A is denoted in the lower part of FIG. 1A.
Based upon the constitution of FIG. 1A, when the distance between a terminal station A and a branching point is longer or shorter than that between another terminal station and the branching point, feeding power between each terminal station becomes in an unbalanced state. For preventing unbalance therebetween, another power feed system of FIG. 1B is devised which can utilize both-end power feed and single-end power feed.
In FIG. 1B, a branching point can be selectively connected to ground from either a terminal station B or C and both-end power feed is carried out between the terminal A and the terminal B where the terminal station C is connected to ground.
The potential level in such a case is denoted in the lower part of FIG. 1B.
This power feed system also can implement a both-end power feed between the terminal stations A and C and a single-end power feed at the terminal station B. The merit of the system is that, even if the distance between at least two points, i.e., a terminal station and a branching point is not equal or is unbalanced, when one terminal station A is connected to a positive power source and the other terminal stations B and C are connected to a negative power source, the power feed between each station can be equal or averaged in the case of power feed between A and B, or between A and C.
The present invention intends to utilize the system constitution of FIG. 1B.
In general, an optical submarine repeater is provided at every several tens of kilometers in a long distance optical transmission line system such as an optical submarine cable transmission line system, and electric power is supplied to an optical submarine repeater which is connected in series from the power unit or the power feed equipment in a constant current power mode. Two kinds of power systems exist. These include a single-end power system fed from only one terminal station of a power unit and a both-end power system fed from a two terminal stations of a power unit. A both-end power system is generally adopted for a long distance transmission line.
In an optical submarine cable transmission line system, an optical transmission line is branched by a branch circuit, and it is possible to provide a system which carries out an optical transmission between three terminal stations. The power feed in this transmission line system carries out a both-end power feed between two terminal stations and a single end power feed by the residual third terminal station. Since a branch unit is laid at the bottom of the sea, the switching between a both-end power feed and a single-end power feed is carried out by a vacuum relay or the like, which is operated by power feed current. Therefore, a demand has arisen for such a power path switching circuit for switching between a both-end power feed and a single end power feed without producing a switching under a high voltage impression condition, because of possible failure in a transmission line and a power feed line.
FIG. 2 is a schematic diagram of a branching point unit with an optical fiber circuit and a power feeding switching circuit according to an embodiment of the present invention.
A signal line and a power feed line for data transmission between optical fiber cables are connected to an optical fiber circuit and a power feed switching circuit, respectively.
FIG. 3 is another constitution of the branching point unit. In FIG. 3, a plurality of signal lines for data transmission is installed and a switching operation for connection can be carried out by the optical fiber switching circuit.
The present invention pertains to the power feed switching circuit of the branching point unit shown in FIG. 2 and FIG. 3.
FIGS. 1A and 1B show only a power feed path and the data transmission line is omitted.
As is obvious in an optical submarine cable transmission line system, since the above-described power path switching circuit is laid at the bottom of the sea, a high reliability is necessary to ensure a continuous operation. Once a contact failure occurs in the power path switching circuit, it is disadvantageous to form a desired power path when a power feed is built-up for a system initialization thereafter.